Rectifier transformer



1938- L. c. NICHOLS 2,127,232

RECTIFIER TRANSFORMER Filed July 25, 1936 3 Sheets-Sheet l Aug. 16,1938. L. c. NICHOLS. v f 2,127,232

RECTIFIER TRANSFORMER Filed July 25, 1936 I 3 Sheets-Sheet 2 Aug. 16,1938.

L. C. NICHOLS RECTIFIER TRANSFORMER Filed July 25, 1936 5 Sheets-Sheet 3Patented Aug. 16, 1938 UNITED STATES PATENT OFFiCE RE GTIFIERTRANSFORMER.

Application July 25, 1936, Serial No. 92,472

10 Claims.

This invention relates in general to improvements in rectifiertransformers, and more particularly to transformers adapted to supplycurrent to groups of electric valves operating in 5 parallel circuits.

It is well known that electric valve converting systems are occasionallysubject to disturbances, such as the so-called backfires resulting frommomentary failure of the valve action of a valve utilized as part of thesystem. In systems utilizing a transformer connecting one or more valveswith an alternating current circuit, such failure particularly resultsin effectively short circuiting the alternating current circuit through15 the transformer, and the latter is then caused to carry an excessivecurrent which may damage the windings thereof by overheating and by theelectromagnetic action thereon of the magnetic leakage fields thereof.It is therefore desirable 20 to so design the transformer as to reducethe magnitude of any backfire currents flowing through the windingsthereof. In particular, when the system presents a plurality of parallelcircuits, the transformer is preferably provided 25 with a secondarywinding divided into parallel sections each connected in one of suchcircuits through a separate valve, such sections being severallyassociated with serially connected sections of the transformer primarywinding. Dur- 30 ing a backfire some of the sections of the primarywinding are thus associated with secondary winding sections which arewithout current, and such primary winding sections then are linked withextensive magnetic leakage fields which materially reduce the flow ofcurrent through the transformer. With such arrangement, current fiow ifalso forcibly initiated simultaneously through all parallel secondarywinding sections, during normal operation of the transformer, and

40 such sections are forced to carry equal amounts of current at everyinstant.

It is, therefore, one of the objects of the present invention to providea transformer for an electric valve converting system having windings 45so arranged that the flow of backfire current therethrough is reduced toa relatively low value.

Another object of the present invention is to provide a transformer foran electric valve converting system having a secondary winding form- 50ing parallel circuits and soarranged that the flow of current isforcibly initiated simultaneously through the several circuits.

Another object of the present invention is to provide a transformer foran electric valve con- 55 verting system having a secondary Windingforming parallel circuits and so arranged that such circuits are forcedto carry equal currents at every instant.

Objects and advantages other than those above set forth will be apparentfrom the following de- 5 scription when read in connection with theaccompanying drawings in which:

Fig. l diagrammatically illustrates the arrangement of the windings andthe connections of a transformer of the shell type forming an embodimentof the present invention and comprising a three-phase primary windingand a six-phase secondary winding divided into three parallel sectionssupplying a group of eighteen valves of an alternating currentrectifying system;

Fig. 2 diagrammatically illustrates another embodiment of the presentinvention differing from the embodiment illustrated in Fig. l in beingprovided with two parallel primary windings and with a six-phasesecondary winding divided into four parallel sections;

Fig. 3 diagrammatically illustrates a further embodiment of the presentinvention consisting of a transformer of the core type having athreephase primary winding and a six-phase secondary winding dividedinto two parallel sections.

It will be understood that some of the features of any one of theembodiments illustrated may also be utilized in combination withfeatures of the other embodimens to form further embodiments of thepresent invention.

Referring more particularly to the drawings by characters of reference,reference numeral 6 in Fig. 1 generally designates a transformer of theso-called shell type adapted to be utilized in conjunction with aplurality of electric valves l to form a converting system such as thesystem illustrated by way of example, which is adapted to rectifyalternating current supplied thereto from a three-phase supply line 8and to deliver the rectified current to a direct current output line 9.Valves l each comprise an anode Hi, the anodes being either eachassociated with a separate cathode, or being associated with a lessernumber of cathodes or even with a single cathode connected with oneconductor of line 9. It will be understood that by providing valves Iwith suitable control electrodes and with a suitable control systemtherefor, the transformer and the valves may also be caused to transmitenergy from line 9 to line 8, or to transmit energy between line 8 andanother alternating current line suitably connected with the transformerand with the valves.

Transformer 6 is provided with a three-phase 55,

core I I on which are arranged the phase portions I2, I3, Id of athree-phase primary winding, each portion consisting of a plurality ofsections such as I211, I22), I20, I2cl serially connected across a pairof conductors of line 8. Means are provided for varying the connectionsbetween the sections of each primary winding phase portion to therebyadjust the secondary voltages of the transformer. Although such resultcould be obtained by changing taps of only one or of less than all thesections of each phase portion, it is generally preferred to provide allsuch sections with taps connected to no load tap changers equal innumber to the number of interconnections between primary: windingsections. In the present embodiment, each primary winding portioncomprises four sections and therefore presents three connections betweensections, which connections may be changed by means of three tapchangers. Only tap changers I6, I1, I8 associated with winding portionI2 are illustrated in detail, the tap changers associated with windingportions I3 and I5 being similarly arranged and connected. Tap changerI6, for example, is provided with a plurality of contacts I9, of whichalternate contacts are severally connected with the taps and with oneterminal of winding section I2a, the remaining segments being severallyconnected with the taps and with one terminal of winding section I2b.Each pair of adjacent taps may be bridged by a brush 2|, the brushes ofthe several tap changers being mounted on a common shaft 22 in orderthat they may be moved simultaneously over the same number of steps ofthe respective tap changers.

The polyphase secondary winding of transformer 6 comprises a pluralityof phase portions 23, 24, 25 each divided into a plurality ofinterconnected parallel sections such as 23a, 23b, 23c interleaved withthe sections of the associated primary winding phase portion I2. Boththe primary and secondary winding sections consist of stacks of diskshaped coils, also called pancake coils, of which only the coils ofwinding portions I2 and 23 are shown in cross section, the supportingmeans therefor being omitted to clarify the drawings. Winding portionsI3, I4, 24, 25 are shown in elevation and are represented as beinginsulated from each other and from core II by means of insulatingspacers 26. Such spacers also serve to brace the windings against eachother and against core II for preventing displacement of the windingsections by the electromagnetic action thereon of the magnetic leakagefields thereof during flow of backfire or short circuit current throughthe transformer. In addition, it is generally preferable to arrange thetaps of each primary winding end section, such as I id, at the end ofsuch section remote from the adjacent secondary winding section such as23a, and to arrange the terminals and the taps of each intermediateprimary winding section, such as I21), near the center of such sectionto thereby remove the taps, which constitute weak points of the winding,from the magnetic leakage fields present in the gaps between adjacentprimary and secondary winding sections.

In order to obtain six-phase current from the transformer secondarywinding, each section thereof, such as 23a, is divided into two portionswhich are symmetrically arranged with respect to the adjacent primarywinding sections, such as I2a, I2b, and which may also be interleaved toreduce the leakage reactance thereof with respect to the associatedprimary winding portion. Each primary winding section is thus arrangedadjacent both portions of at least one of the secondary winding sectionsand has a relatively low leakage reactance with respect thereto, and isalso arranged remote from the remainder of the primary and secondarywinding sections and, therefore, has a relatively high leakage reactancewith respect thereto. The two portions of a sec ondary winding section,such as 23a, are adapted to alternately transmit unidirectional currentimpulses to the associated anodes, such as Hm, I 0d, of valves 1 in thecourse of alternate half cycles of the voltage of line 8. The operationof the secondary winding sections is preferably controlled by means ofan-interphase transformer 27 connected therewith and forming therewith,in effect, a unitary transformer structure, as is well known in the art.

In operation, line 8 being energized, current is drawn from line 8sequentially through winding portions I2, 13 and I4, and the currentsinduced thereby in winding portions 23, 24 and 25 are converted, by theaction of valves 1, into successive unidirectional impulses whichcombine at the common cathode of valves I to form a flow of directcurrent supplied to line 9. At every instant, three valves receivecurrent from the associated parallel sections of one of winding portions23, 24 and 25, the action of interphase transformer 21 causing the flowsof current which are successively initiated in the different groups ofvalves to overlap by one-half of their duration, so that current iscarried at every instant by at least six valves. Considering suchoperation in greater detail, at a particular moment of the voltage cycleof line 8, the voltage conditions of such line are such that threevalves 1 cease carrying current, and a flow of current is thenestablished simultaneously through three valves I such, for example, asthe valves comprising anodes Illa, I fig and Him respectively associatedwith parallel portions of winding sections 23a, 23b and 230. The threeparallel circuits established through such winding portions are similarto one another and receive equal voltages, so that normally the flow ofcurrent is established therethrough simultaneously.

If one of the circuits, such as the circuit including anode Illa and theassociated winding portion 23a, fails to carry current for any reasonsuch as non-uniform conditions of pressure and temperature in thevalves, the primary winding portions I2a and I2b adjacent to section 23acause the establishment of a magnetic leakage flux therethrough, suchleakage flux closing itself about winding section I2a through a. portiononly of core II and through winding section 23a. Winding section Inaccordingly takes an increased fraction of the voltage of line 8 and, asa result of the series connection of winding portion I2, windingsections I22), I2c, I2d thereof receive a lesser fraction of the voltageof line 8 and link with a reduced magnetic flux, whereby the voltagesinduced in adjacent winding sections 23b and 230 decrease while thevoltage induced in section 23a rises to a value sufficient to overcomethe cause of the failure of section 2311 to carry current, thus forcingthe substantially simultaneous initiation of the flow of current throughall three parallel sections. Such action would also take place in asimilar manner, if two of the three parallel circuits tended to remainwithout current, to increase the voltages impressed on the twomomentarily inoperative circuits and thus restore normal operatingcondition.

By a process similar to that above described, if the currents in theparallel circuits become unbalanced, the voltage impressed on thecircuit carrying the smallest current is increased by an increase of themagnetic flux linking therewith, while the voltage impressed on thecircuit carrying the highest current is decreased by a decrease of themagnetic flux linking therewith; such adjustment of the magnetic fluxesbeing obtained automatically by the distribution of the leakage fluxesproduced by the serially connected primary winding sections.

The occurrence of a backfire in valves 1 would result from the loss ofthe valve action of one of the valves, of which the anode may thenbecome a cathode. Assuming that anode lfla, for example, becomes a;cathode, current may flow thereto from all other anodes except theanodes normally operating in parallel therewith whereby line 8 is shortcircuited through the transformer. As is well known, a backfiring anodemay receive current simultaneously from several of the secondary phasecircuits of the transformer at every instant. For example, at aparticular moment of the voltage cycle of line 8, current may flow fromthe upper terminal of interphase transformer 21 through one portion ofeach of the parallel sections of winding portion 24 and the associatedanodes to anode Illa and the associated portion of winding section 23aback to the upper terminal of interphase transformer 21 and also fromthe lower terminal of the interphase transformer through one portion ofeach of the parallel sections of winding portion 25 and the associatedanodes through anode Illa, the associated portion of winding section2311, and through the interphase transformer. As is usual in theoperation of transformers, such currents are induced in the secondarywinding portions by the associated primary winding portions. During suchoperation, winding sections 231) and 230 are without current. Primarywinding sections I20 and lZd may thus establish extensive magneticleakage fields about themselves and through secondary winding sections23d and 230 and, as the result of the serial connection of windingsections Her and I21) with sections I20 and l2d, the latter function inthe same manner as windings of independent reactors connected in serieswith winding sections l2a, I221. The flow of current through windingportion [2 is thereby considerably reduced, and the magnitude of theflow of backfire current between winding portions 23, 24 and 25 is thusreduced to a material extent.

If generators or converting systems other than the systems shown areconnected to supply current to line 8, the occurrence of a backfire atanode l a also causes direct current to flow from line 9 through thecommon cathode of valves 1, then functioning as an anode, through anodeIlla, the associated portion of winding section 2311 and one winding ofinterphase transformer 21 to the other conductor of line 9. Such currentis not established instantly at a constant value and, during the rise ofthe value thereof, the flow of such current through winding section 23atends to induce a similar rising flow of current through winding portionI2. The magnetic leakage fields established about winding sections [20and [2d, however, oppose the establishment of such current in windingportion I2, thereby also reducing the rate of increase of the current inwinding section 23a. Such current may therefore be interrupted by meansof suitable switching means before hav-- ing reached the maximum valuethereof, such maximum value being determined by the resistance of thecircuit traversed thereby. The flow of backfire current caused byfailure of the valve action of anodes other than anode lOa would bereduced in the manner above set forth as a result of the serialconnection of the sections of winding portions l2, l3 and I l. Theheating and stressing of the conductors of the transformer windings arethus considerably reduced, and the thrusts impressed on the windingsections by the electromagnetic action of the magnetic leakage fieldsthereof are reduced to values such that the sections may be held inplace by means of spacers 26.

In the embodiment illustrated in Fig. 2 core H is provided with athree-phase primary winding, of which each phase portion such as 28comprises four sections such as 28a, 28b, 28c, 28d connected in seriesparallel connection through tap changers such as 29 and 3|. The tapchangers are illustrated as being each provided with an odd number ofsegments to obtain an even number of steps, the two winding sectionsbeing connected with one tap changer which is then provided with numbersof taps differing by one. In the present embodiment, each secondaryphase portion such as 32 is divided into four sections such as 32a, 32b,32c, 3201 each divided into two portions supplying two valves 1, therebeing accordingly twenty-four valves which are preferably divided intotwo equal groups each provided with a separate cathode to form aseparate structure or rectifier. It is generally preferable to controlthe operation of the winding sections associated with differentrectifiers by means of separate interphase transformers such astransformers 33 and 34. The operation of the serially connected primarywinding sections in causing the currents through the associated parallelsecondary winding sections to be initiated simultaneously and to bemaintained at equal values, and in limiting the flow of backfire currentthrough the transformer, is similar to that set forth with respect tothe embodiment illustrated in Fig. 1.

In the embodiment illustrated in Fig. 3, the transformer is assumed tobe provided with a core 36 adapted to receive coextensive phase windingportions arranged side by side about different legs of the core to forma transformer of the so-called core type. Each primary winding phaseportion, such as 31, is divided into a plurality of sections such as31a, 31b each Wound about one of the sections such as 38a, 38b of asecondary phase winding portion 38. Each winding phase portion is shownas being divided into only two sections whereby the transformer isoperable to supply current to a group of twelve valves operating inparallel in pairs, but it will be understood that a greater number ofsections may also be utilized as in the embodiments illustrated in Figs.1 and 2. The two sections of each primary winding phase portion may beconnected through a single tap changer such as at 39. The operation ofthe serially connected primary winding sections in causing the currentsin the associated parallel secondary winding section to be initiatedsimultaneously and to be maintained at equal values and in limiting theflow of backfire current through the transformer, is similar to thatabove set forth with respect to the embodiment illustrated in Fig. 1.

It will be observed that, in the present embodiment, the two windingsections such .as 31a, 31b of a primary winding phase portion as well asthe two sections such as 38a and 38b of the associated secondary windingphase portion are alined end to end on a core leg and each consists of aplurality of nested cylindrical coils. It is well known that such coilscannot be braced satisfactorily against the core to withstand axialthrusts resulting from the action of the magnetic leakage fieldestablished thereabout during a backfire. For example, if an anodeconnected with winding section 38a loses its valve action, during a partof the cycle of the voltage of line 8 a large current flows from atleast one of the secondary winding portions other than portion 38 andthrough the associated anode or anodes of valves 1 through anode Illaand the associated portion of section 38a, while section 3% remainswithout current. Both portions of primary winding portion 3'!necessarily carry equal currents at such time and, section 38a beingarranged dissymmetrically with respect to the entire winding portion 31,the magnetic leakage field of winding portion 31 tends to exert a largeaxial thrust on winding section 38a which would displace such sectionbodily on core 36. To avoid such result, means are arranged between thewinding sections for diverting the magnetic leakage field of eachprimary winding section and of the adjacent secondary winding sectionfrom all other winding sections. Such means are thus essentiallymagnetic shields which may consist of additional yokes 4| of core 36separating the top and bottom winding sections or of other equivalentmeans such as disks of magnetic material inserted between the top andbottom winding sections Each winding section is thus subject to onlymagnetic leakage fields which are symmetrical with respect thereto andwhich do not exert .any axial thrust thereon.

Although but a few embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various modifications and changes may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

1. A transformer for an electric valve converting system comprising aprimary winding having a phase portion thereof divided into a pluralityof serially connected sections arranged on a common core, and asecondary winding having a plurality of interconnected parallel sectionsarranged on said core and each divided into two portions adapted toalternately transmit unidirectional current impulses, each said primarywinding section being arranged adjacent both portions of at least one ofsaid secondary winding sections and having a relatively low leakagereactance with respect thereto and being arranged remote from theremainder of said primary and secondary winding sections and having arelatively high leakage reactance with respect thereto.

2. A transformer for an electric valve converting system comprising apolyphase primary winding having each phase portion thereof divided intoa plurality of serially connected sections, and a polyphase secondarywinding having each phase portion thereof divided into a plurality ofparallel sections, each primary winding section being arranged adjacentat least one of said secondary winding sections and having a relativelylow leakage reactance with respect thereto and being arranged remotefrom the remainder of said primary and secondary winding sections andhaving .a relatively high leakage reactance with respect thereto tothereby limit the fioW of backfire current between said secondary phasep0rtions.

3. A transformer structure for an electric valve converting systemcomprising a polyphase primary winding having each phase portion thereofdivided into a plurality of serially connected sections, a polyphasesecondary winding having each phase portion thereof divided into aplurality of parallel sections, each primary winding section beingarranged adjacent at least one of said secondary winding sections andhaving a relatively low leakage reactance with respect thereto and beingarranged remote from the remainder of said primary and secondary windingsections and having a relatively high leakage reactance with respectthereto to thereby limit the flow of backfire current between saidsecondary phase portions, and interphase windings connected with saidsecondary winding for controlling the operation thereof.

i. A transformer for an electric valve converting system comprising aprimary winding having a plurality of serially connected sectionsarranged on a common core, a secondary winding having a plurality ofinterconnected parallel sections arranged on said core and each dividedinto two portions adapted to alternately transmit unidirectional currentimpulses, each said primary winding section being arranged adjacent bothportions of one of said seconary winding sections and having arelatively low leakage reactance with respect thereto and being arrangedremote from the remainder of said primary and secondary winding sectionsand having a relatively high leakage reactance with respect thereto, andmeans arranged between said winding sections for diverting the magneticleakage fields of each said primary winding section and of the adjacentsaid secondary winding section from all other said winding sections.

5. A transformer for an electric valve converting system comprising aprimary winding having a plurality of serially connected sectionsarranged on a common core, a secondary winding .1-

having a plurality of interconnected parallel sections arranged on saidcore and each divided into two portions adapted to alternately transmitunidirectional current impulses, each said primary winding section beingarranged adjacent both portions of at least one of said secondarywinding sections and having a relatively low leakage reactance withrespect thereto and being arranged remote from the remainder of saidprimary and secondary winding sections and having a relatively highleakage reactance with respect thereto, said primary and secondarywinding sections being interleaved, and means for bracing said windingsections against each other and against said core for preventingdisplacement of said winding sections by electromagnetic action thereonof the magnetic leakage fields thereof during flow of backfire currentthrough the transformer.

6. A transformer for an electric valve converting system comprising aprimary winding having a phase portion thereof divided into a plLu'alityof sections arranged in series parallel connection and arranged on acommon core, and a secondary winding having a plurality ofinterconnected parallel sections arranged on said core and each dividedinto two portions adapted to alternately transmit unidirectional currentimpulses, each said primary winding section being arranged adjacent bothportions of one of said secondary winding sections and having arelatively low leakage reactance with respect thereto and being arrangedremote from the remainder of said pri mary and secondary windingsections and having a relatively high leakage reactance with respectthereto.

'7. A transformer for an electric valve converting system comprising aprimary winding having a plurality of serially connected sectionsarranged on a common core, a secondary winding having a plurality ofinterconnected parallel sections arranged on said core and each dividedinto two portions adapted to alternately transmit unidirectional currentimpulses, each said primary winding section being arranged adjacent bothportions of at least one of said secondary winding sections and having arelatively low leakage reactance with respect thereto and being arrangedremote from the remainder of said primary and secondary winding sectionsand having a relatively high leakage reactance with respect thereto, andmeans for adjusting the voltages of said secondary winding comprisingmeans for varying the connections between said primary winding sections.

8. In an electric current converting system, the combination with asource of electric current, and electric valve means comprising aplurality of anodes, of means for causing the flow of currents suppliedfrom said source of predetermined relative magnitudes simultaneouslythrough said anodes and for opposing changes in magnitude of the flow ofcurrent through any one of said anodes relative to the magnitude of theflow of current through another thereof comprising a transformer windingphase portion divided into a plurality of interconnected parallelsections severally connected with said anodes, and another transformerwinding portion connected with said source of current and divided into aplurality of serially connected sections severally closely inductivelycoupled with at least one of said interconnected parallel sections andrelatively loosely coupled with the remainder of the said windingsections.

9. In an electric current converting system,

the combination with a source of electric current, and electric valvemeans comprising a plurality of anodes, of means for causing the flow ofcurrents supplied from said source of predetermined relative magnitudessimultaneously through said anodes and for opposing changes in themagnitude of the flow of current through any one of said anodes relativeto the magnitude of the flow of current through another of said anodescomprising a transformer winding phase portion divided into a pluralityof interconnected parallel sections severally connected with said anodesand positioned on a common core, and another transformer Winding phaseportion connected with said source of current and divided into aplurality of serially connected sections severally positioned on saidcore adjacent at least one of said interconnected parallel sections andhaving relatively low leakage reactance with respect thereto and beingpositioned remote from the remainder of the first and second saidwinding sections and having a relative high leakage reactance withrespect thereto.

10. In an electric current converting system, the combination with asource of electric current, and electric valve means comprising aplurality of anodes, of means for causing the flow of currents suppliedfrom said source of predetermined relative magnitudes simultaneouslythrough said anodes and for opposing changes in magnitude of the flow ofcurrent through any one of said anodes relative to the magnitude of theflow of current through another thereof comprising a transformer windingphase portion divided into a plurality of interconnected parallelsections severally connected with said anodes, and another transformerwinding connected with said source of current having a phase portionthereof divided into a plurality of sections,

in series parallel connection severally relatively closely inductivelycoupled with at least one of said interconnected parallel sections andrelatively loosely coupled with the remainder of said winding sections.

LOUIS C. NICHOLS.

